Preparation of ethylene glycol

ABSTRACT

A process for preparing ethylene glycol wherein a mixture of carbon monoxide and hydrogen is contacted at an elevated temperature and pressure and in the presence of a solvent with a ruthenium compound and a promoter, such as pyrocatechol. In another aspect this invention relates to the preparation of ethylene glycol ethers from carbon monoxide and hydrogen.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for preparing ethylene glycol byreaction of carbon monoxide and hydrogen in the presence of a catalyst,a promoter and a solvent. In another embodiment, this invention isconcerned with the preparation of ethylene glycol ethers from carbonmonoxide and hydrogen.

2. Prior Art

In recent years, a large number of patents have been issued dealing withthe synthesis of lower molecular weight hydrocarbons, olefins, alkanolsetc. from synthesis gas. Of particular note, U.S. Pat. No. 2,636,046,discloses the synthesis of polyhydric alcohols and their derivatives byreaction between carbon monoxide and hydrogen at elevated pressures(>1500 atm or 22000 psi) and temperatures of >150° C. using certaincobalt-containing catalysts. The reaction of carbon monoxide andhydrogen in the presence of a ruthenium catalyst and a pyridine baseligand to form ethylene glycol is set out in U.S. Pat. No. 4,170,605.Also recently, in Belgium Pat. No. 793,086 and U.S. Pat. No. 3,940,432there is described the co-synthesis of methanol and ethylene glycol frommixtures of carbon monoxide and hydrogen using a rhodium complexcatalyst. Typically, CO-hydrogenation is effected at 8000 psi of 1:1 H₂/CO synthesis gas, at 220° C., using tetraglyme as the solvent, anddicarbonylacetylacetonatorhodium(I) in combination with promoters suchas pyridine and its derivatives as the catalyst precursor. (For summaryof the work, see: R. L. Pruett, Annals New York Academy of Sciences,Vol. 295 p. 239 (1977)). While other metals of Group VIII of thePeriodic Table have been tested for activity under similar conditions,including cobalt, ruthenium, copper, manganese, iridium and platinum,only cobalt was found to have slight activity. The use of rutheniumcompounds in particular failed to produce polyfunctional products suchas ethylene glycol. This is illustrated in U.S. Pat. No. 3,833,634 forsolutions of triruthenium dodecacarbonyl.

SUMMARY OF THE INVENTION

In this invention ethylene glycol is prepared by reaction of carbonmonoxide and hydrogen in the presence of a ruthenium compound, apromoter and a solvent at an elevated temperature and pressure. Inanother embodiment, this invention relates to the production of ethyleneglycol ethers by reaction of carbon monoxide and hydrogen in thepresence of a ruthenium compound, a promoter and a mineral acid.

Surprisingly, it has been found that when the reaction of carbonmonoxide and hydrogen is conducted in the presence of a rutheniumcompound and a promoter, such as pyrocatechol, polyfunctional productsare formed.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a process for preparing ethylene glycol whichcomprises reacting a mixture of hydrogen and carbon monoxide in thepresence of a ruthenium compound and a promoter at a temperature ofabout, 125° to about 300° C. and at a pressure of about 1000 psi toabout 10,000 psi and wherein the reaction is conducted in the presenceof a solvent of the formula:

    R(OCH.sub.2 CH.sub.2).sub.n OR'

wherein R is alkyl having from 1 to 4 inclusive carbon atoms and R' isselected from the group consisting of hydrogen and alkyl having from 1to 4 inclusive carbon atoms, and n is an integer of from 2 to 4inclusive.

In another aspect this invention relates to a process for preparingethylene glycol ethers which comprises reacting a mixture of carbonmonoxide and hydrogen in the presence of a ruthenium compound catalystand a promoter at a temperature of about 125° to about 300° C. and at apressure of about 1000 to about 10,000 psi and wherein the reaction isconducted in the presence of a solvent and a mineral acid.

The ruthenium compound catalyst employed in the process of thisinvention may be chosen from a wide variety of organic inorganiccompounds, complexes, etc., as will be shown and illustrated below. Itis only necessary that the ruthenium compound utilized contain rutheniumin any of its normal oxidation states. The actual catalytically activespecies is believed to comprise ruthenium in complex combination withcarbon monoxide and hydrogen.

The ruthenium may be added to the reaction mixture in an oxide form, asin the case of, for example, ruthenium(IV) oxide, hydrate, anhydrousruthenium(IV) dioxide and ruthenium(VIII) tetraoxide. Alternatively, itmay be added as the salt of a mineral acid, as in the case ofruthenium(III) chloride hydrate, ruthenium(III) bromide, anhydrousruthenium(III) chloride and ruthenium nitrate, or as the salt of asuitable organic carboxylic acid (see below), for example,ruthenium(III) acetate, ruthenium(III) propionate, ruthenium butyrate,ruthenium(III) trifluoroacetate, ruthenium octanoate, rutheniumnapththenate, ruthenium valerate and ruthenium(III) acetylacetonate. Theruthenium may also be added to the reaction zone as a carbonyl orhydrocarbonyl derivative. Here, suitable examples include trirutheniumdodecacarbonyl, hydrocarbonyls such as H₂ Ru₄ (CO)₁₃ and H₄ Ru₄ (CO)₁₂,and substituted carbonyl species such as the tricarbonylruthenium(II)chloride dimer, [Ru(CO)₃ Cl₂ ]₂.

In a preferred embodiment of the invention ruthenium is added to thereaction zone as one or more oxide, salt or carbonyl derivative speciesin combination with one or more Group VB, as set out on page 125 ofMellor's, Modern Inorganic Chemistry, 1967, tertiary donor ligands. Thekey elements of the Group VB ligands include nitrogen, phosphorous,arsenic and antimony. These elements, in their trivalent oxidationstates, particularly tertiary phosphorous and nitrogen, may be bonded toone or more alkyl, cycloalkyl, aryl, substituted aryl, aryloxide,alkoxide and mixed alkaryl radicals, each containing from 1 to 12 carbonatoms, or they may be part of a heterocyclic ring system, or be mixturesthereof. Illustrative examples of suitable ligands that may be used inthis invention include: triphenylphosphine, tri-n-butylphosphine,triphenylphosphite, triethylphosphite, trimethylphosphite,trimethylphosphine, tri-p-methoxyphenylphosphine, triethylphosphine,trimethylarsine, triphenylarsine, tri-p-tolylphosphine,tricyclohexylphosphine, dimethylphenylphosphine, trioctylphosphine,tri-o-tolyphosphine, 1,2-bis(diphenylphosphino)ethane, triphenylstibine,trimethylamine, triethylamine, tripropylamine, tri-n-octylamine,pryidine, 2,2'-dipyridyl, 1,10-phenanthroline, quinoline,N,N'dimethylpiperazine, 1,8-bis(dimethylamino)naphthalene andN,N-dimethylaniline.

One or more of these ruthenium-tertiary Group VB donor ligandcombinations may be preformed, prior to addition to the reaction zone,as in the case, for example, of tris(triphenylphosphine)ruthenium(II)chloride and dicarbonylbis(triphenylphosphine)ruthenium(II) chloride oralternatively, said complexes may be formed in situ.

The quantity of ruthenium catalyst employed in the instant invention isnot critical and may vary over a wide range. In general, the novelprocess is desirably conducted in the presence of a catalyticallyeffective quantity of one or more of the active ruthenium speciestogether with the promoter which gives the desired products inreasonable yields. The reaction proceeds when employing as little asabout 0.001 weight percent and even lesser amounts of ruthenium, basisthe total weight of the reaction mixture. The upper concentration isdictated by a variety of factors including catalyst cost, partialpressures of carbon monoxide and hydrogen, operating temperature, etc. Aruthenium catalyst concentration of from about 0.01 to about 10 weightpercent ruthenium, based on the total weight of reaction mixture, isgenerally desirable in the practice of this invention.

Promoters useful in the process of this invention include polyhydricphenols such as pyrocatechol, resorcinol, quinol, pyrogallol,hydroxyquinol, phloroglucinol, alkylated dihydroxybenzenes such asorcinol, dihydroxynaphthalenes and diphenols such as O,O'-diphenol aswell as mixtures of these materials.

The number of gram moles of the promoter employed per gram atom ofruthenium can be varied widely and is generally in the range of about0.1 to about 100 and preferably from about 1.0 to about 10.

Solvents suitable for use in the process of this invention have theformula:

    R(OCH.sub.2 CH.sub.2).sub.n OR'

wherein R is alkyl having 1 to 4 inclusive carbon atoms and R' isselected from the group consisting of hydrogen and alkyl having from 1to 4 inclusive carbon atoms as exemplified by diethylene glycolmonomethyl ether, diethylene glycol dimethyl ether, diethylene glycolmonoethyl ether, diethylene glycol diethyl ether, diethylene glycolmonobutyl ether, diethylene glycol dibutyl ether, triethylene glycoldimethyl ether, tetraethylene glycol dimethyl ether, tetraethyleneglycol monopropyl ether, etc.

In the embodiment of this invention relating to the process forpreparing ethylene glycol ethers by reaction of carbon monoxide andhydrogen conducted in the presence of a ruthenium compound, a promoter,solvent and a mineral acid, the suitable mineral acids include sulfuricacid, hydrochloric acid and phosphoric acid. The number of gram moles ofthe mineral acid used per gram atom of ruthenium can be varied over awide range and generally will be in the range of about 1.0 to about 100.

The temperature range which can usefully be employed in this process isa variable dependent upon other experimental factors, including thepressure, and the concentration and choice of particular species of theruthenium-containing compound and the promoter among other things. Therange of operability is from about 125° to about 300° C. whensuperatmospheric pressures of syngas are employed. A narrower range ofabout 150° to about 250° C. represents the preferred temperature range.

Superatmospheric pressures of 1000 psi or greater lead to substantialyields of the desired ethylene glycol or glycol ethers by the process ofthis invention. A preferred operating range is from about 1500 psi toabout 7500 psi, although pressures above 7500 psi also provide usefulyields of the desired end products. The pressures referred to hererepresent the total pressure generated by all the reactants, althoughthey are substantially due to the carbon monoxide and hydrogen fractionsin these examples.

The relative amounts of carbon monoxide and hydrogen which may beinitially present in the syngas mixture are variable, and these amountsmay be varied over a wide range. In general, the mole ratio of CO:H₂ isin the range from about 20:1 up to about 1:20, preferably from about 5:1to 1:5, although ratios outside these ranges may also be employed.Particularly in continuous operations, but also in batch experiments,the carbon monoxide-hydrogen gaseous mixtures may also be used inconjunction with up to 50% by volume of one or more other gases. Theseother gases may include one or more inert gases such as nitrogen, argon,neon and the like, or they may include gases that may, or may not,undergo reaction under CO hydrogenation conditions, such as carbondioxide, hydrocarbons such as methane, ethane, propane and the like,ethers such as dimethyl ether, methylethyl ether and diethyl ether.

In all these syntheses in order to achieve a high degree of selectivitythe amount of carbon monoxide and hydrogen present in the reactionmixture should be sufficient to at least satisfy the stoichiometryinvolved in forming the desired ethylene glycol or corresponding ethers.Excess carbon monoxide and/or hydrogen over the stoichiometric amountsmay be present, if desired.

The novel process of this invention can be conducted in a batch,semi-continuous or continuous fashion. The catalyst may be initiallyintroduced into the reaction zone batchwise, or it may be continuouslyor intermittently introduced into such a zone during the course of thesynthesis reaction. Operating conditions can be adjusted to optimize theformation of the desired ethylene glycol or glycol ether products, andsaid material may be recovered by methods well known in the art, such asdistillation, fractionation, extraction and the like. A fraction rich inthe ruthenium catalyst and promoter may then be recycled to the reactionzone, if desired, and additional products generated.

The products have been identified in this work by one or more of thefollowing analytical procedures, viz, gas-liquid phase chromatography(GLC), Fourier Transform infrared spectrometry (FTIR), nuclear magneticresonance (nmr) and elemental analyses, or a combination of thesetechniques. Analyses have, for the most part, been by parts in weight;all temperatures are in degrees centigrade and all pressures in poundsper square inch gauge (psi).

The following examples which illustrate various embodiments of theinvention are to be considered not limitative.

EXAMPLE I

To a degassed sample of tetraglyme, i.e., CH₃ (OCH₂ CH₂)₄ OCH₃ (25 g)contained in a glass-lined reactor equipped for pressurizing, heatingand means of addition was added, under a nitrogen environment,tris(triphenylphosphine)ruthenium(II) chloride (0.96 g, 1.0 mmole) andpyrocatechol (0.88 g, 8 mmoles). The reactor was sealed, flushed with amixture of carbon monoxide and hydrogen (1:1 molar) and pressured to2000 psi with the same gaseous mixture. The reactor was heated to 220°with rocking, and the pressure raised to 6300 psi through the additionof the gaseous mixture (1:1 molar CO/H₂) from a large surge tank afterwhich the reactor was held at 220° C. for 18 hours.

Upon cooling and depressuring of the reactor, 28.1 g of clear, deep red,liquid product was recovered. There was no solid fraction. Analysis ofthe liquid product by GLC and FTIR techniques on a solvent free basisgave the following results:

    ______________________________________                                        COMPOUND      SELECTIVITY, WT. %                                              ______________________________________                                        Ethylene Glycol                                                                             11                                                              Methanol      42                                                              Ethanol       8                                                               Methyl Formate                                                                              5                                                               Water         11                                                              ______________________________________                                    

The remainder of the sample was primarily pyrocatechol together withunidentified materials.

Samples of off-gas typically showed the following composition:

43% hydrogen

53% carbon monoxide

2.3% carbon dioxide

EXAMPLE II

The procedure of Example I was followed with the exception that 0.244 gof dicarbonylbis(triphenylphosphine)-ruthenium(II) chloride was used asthe ruthenium source.

The liquid product, recovered from the reactor after the 18 hourreaction period, when analyzed by GLC on a solvent free basis gave thefollowing results:

    ______________________________________                                        COMPOUND      SELECTIVITY, WT. %                                              ______________________________________                                        Ethylene Glycol                                                                             5                                                               Methanol      14                                                              Ethanol       3                                                               Water         8                                                               Methyl Formate                                                                              5                                                               ______________________________________                                    

Samples of off-gas from this run typically showed the followingcomposition:

43% hydrogen

55% carbon monoxide

1.2% carbon dioxide

EXAMPLE III

The procedure of Example I was followed with the exception thatruthenium(III) acetylacetonate (0.398 g, 1.0 mmole) provided the sourceof ruthenium.

The products of the reaction were essentially the same as in Example Iand analysis of the liquid product showed the following weight percentselectivities:

    ______________________________________                                        COMPOUND      SELECTIVITY WT. %                                               ______________________________________                                        Ethylene glycol                                                                             3                                                               Methanol      24                                                              Methyl Formate                                                                              3                                                               Water         13                                                              ______________________________________                                    

The remainder of the sample was primarily pyrocatechol plus unidentifiedmaterials.

Samples of off-gas from this run typically showed the followingcomposition:

44% hydrogen

55% carbon monoxide

1.5% carbon dioxide

EXAMPLE IV

The procedure of Example I was followed with the exception thatruthenium dodecacarbonyl (0.213 g, 1.0 mmole Ru) was the source ofruthenium and 1.67 g of sulphuric acid (95%) was added to the tetraglymesolvent. The reaction was allowed to proceed for 6 hours at 220° C.

The deep red liquid product (27.7 g) recovered again showed no evidenceof solid precipitate. An analysis by GLC and FTIR gave the followingselectivities on a solvent free basis:

    ______________________________________                                        COMPOUND            SELECTIVITY, WT. %                                        ______________________________________                                        Ethylene Glycol monomethyl ether                                                                  12                                                        Ethylene glycol dimethyl ether                                                                    12                                                        Methanol            9                                                         Water               39                                                        ______________________________________                                    

The remainder of the sample was primarily pyrocatechol, 1,4-dioxane andunidentified materials.

What is claimed is:
 1. A process for the preparation of ethylene glycolwhich comprises reacting carbon monoxide and hydrogen in the presence ofa ruthenium compound and one or more polyhydric phenols at a temperatureof about 125° to about 300° C. and at a pressure of about 1000 psi toabout 10,000 psi and wherein the said reaction is conducted in thepresence of a solvent having the formula:

    R(OCH.sub.2 CH.sub.2).sub.n OR'

wherein R is alkyl having 1 to 4 inclusive carbon atoms and R' isselected from the group consisting of hydrogen and alkyl having 1 to 4inclusive carbon atoms, and n is an integer of from 2 to 4 inclusive. 2.The process of claim 1 wherein the reaction is conducted in the presenceof polyhydric phenol selected from the group consisting of pyrocatechol,resorcinol, quinol, pyrogallol, hydroxyquinol, phloroglucinol, orcinol,dihydroxynaphthalene and 0,0'-diphenol.
 3. The process of claim 1wherein the said reaction is conducted at a temperature of about 150° toabout 250° C.
 4. The process of claim 1 wherein the said reaction isconducted at a pressure of about 1500 psi to about 7500 psi.
 5. Theprocess of claim 1 wherein the said ruthenium compound is selected fromthe group consisting of tris(triphenylphosphine)ruthenium(II) chloride,dicarbonyl-bis(triphenylphosphine)ruthenium(II) chloride, ruthenium(III)acetylacetonate and ruthenium dodecacarbonyl.
 6. The process of claim 1wherein the said ruthenium compound istris(triphenylphosphine)ruthenium(II) chloride.
 7. The process of claim1 wherein the said ruthenium compound isdicarbonylbis(triphenylphosphine)-ruthenium(II) chloride.
 8. The processof claim 1 wherein the said ruthenium compound is ruthenium(III)acetylacetonate.
 9. The process of claim 1 wherein the said rutheniumcompound is ruthenium dodecacarbonyl.
 10. The process of claim 1 whereinthe said solvent is CH₃ (OCH₂ CH₂)₂ OCH₃.
 11. The process of claim 1wherein the said solvent is CH₃ (OCH₂ CH₂)₄ OCH₃.
 12. The process ofclaim 1 wherein the said promoter is pyrocatechol.
 13. The process ofclaim 1 wherein the said ruthenium compound istris(triphenylphosphine)ruthenium(II) chloride, the said promoter ispyrocatechol and the said solvent is CH₃ (OCH₂ CH₂)₄ OCH₃.
 14. Theprocess of claim 1 wherein the said ruthenium compound isdicarbonylbis(triphenylphosphine)-ruthenium(II) chloride, the saidpromoter is pyrocatechol and the said solvent is CH₃ (OCH₂ CH₂)₄ OCH₃.15. The process of claim 1 wherein the said ruthenium compound isruthenium(III) acetylacetonate, the said promoter is pyrocatechol andthe said solvent is CH₃ (OCH₂ CH₂)₄ OCH₃.